1. Field of the Invention
The present invention relates to a photosensor having a high sensitivity which can be easily manufactured and to a method of manufacturing such a photosensor. The photosensor according to the invention is applied to, for example, a photometric device of cameras, a distance measuring device, or the like.
2. Description of the Prior Art
Photodiodes, phototransistors, or the like are generally used as photoelectric converting elements. However, since the sensitivity which is derived by use of only such a photoelectric converting element is insufficient, the sensitivity is ordinarily improved by connecting an amplifier to this element.
However, conventional photosensor are constituted in such a manner that the photoelectric converting element and amplifier are formed on different substrates and they are connected by way of wirings such as wire bonding. Consequently, a connection leakage current exists between the photoelectric converting element and the amplifier. Therefore, particularly, in the case of low illuminance (less than about 10.sup.-3 luxes) at which a photocurrent which is produced in the photoelectric converting element is very small, the S/N ratio (signal to noise ratio) is degraded.
As a photosensor to solve such a drawback, there has been proposed a photosensor in which a photoelectric converting element and an amplifier are integrally formed (Japanese Patent Examined Publication (Kokoku) No.27104/1984 and U.S. Pat. No. 4,488,038).
However, according to the invention disclosed in the Japanese Patent Examined Publication (Kokoku) No.27,104/1984, the photoelectric converting element is integrally formed with an IIL gate. Therefore, in the case where the photocurrent becomes very small since the illuminance is low, the ratio between an injection current and a signal current becomes large, so that the output signal becomes unstable.
On one hand, according to the invention set forth in U.S. Pat. No. 4,488,038, a transistor of the Schottky barrier type and the like are used, so that special manufacturing processes are needed.